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 $111.70   8.603%   $121.3096   $121.31   $121.30   $121.30  
  Purchase #2 $59.60   4.385%   $62.2135   $62.21   $62.20   $62.20  
  Purchase #3 $26.46   9.570%   $28.9922   $28.99   $29.00   $29.00  
  Purchase #4 $205.25   8.860%   $223.4352   $223.44   $223.45   $223.40  
  Purchase #5 $244.29   8.828%   $265.8559   $265.86   $265.85   $265.90  
  Purchase #6 $110.58   11.310%   $123.0866   $123.09   $123.10   $123.10  
  Purchase #7 $188.88   6.825%   $201.7711   $201.77   $201.75   $201.80  
  7 purchase totals = $946.76       $1,026.6641   $1,026.67   $1,026.65   $1,026.70