Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.39   7.279%   $223.5587   $223.56   $223.55   $223.60  
  Purchase #2 $119.88   6.642%   $127.8424   $127.84   $127.85   $127.80  
  Purchase #3 $213.44   10.474%   $235.7957   $235.80   $235.80   $235.80  
  Purchase #4 $211.27   9.227%   $230.7639   $230.76   $230.75   $230.80  
  Purchase #5 $246.81   6.834%   $263.677   $263.68   $263.70   $263.70  
  Purchase #6 $103.96   13.855%   $118.3637   $118.36   $118.35   $118.40  
  Purchase #7 $155.44   8.734%   $169.0161   $169.02   $169.00   $169.00  
  7 purchase totals = $1,259.19       $1,369.0175   $1,369.02   $1,369.00   $1,369.10