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 $191.85   8.382%   $207.9309   $207.93   $207.95   $207.90  
  Purchase #2 $238.45   7.466%   $256.2527   $256.25   $256.25   $256.30  
  Purchase #3 $44.63   7.573%   $48.0098   $48.01   $48.00   $48.00  
  Purchase #4 $225.44   7.674%   $242.7403   $242.74   $242.75   $242.70  
  Purchase #5 $138.96   8.400%   $150.6326   $150.63   $150.65   $150.60  
  Purchase #6 $167.54   4.279%   $174.709   $174.71   $174.70   $174.70  
  Purchase #7 $117.95   7.740%   $127.0793   $127.08   $127.10   $127.10  
  7 purchase totals = $1,124.82       $1,207.3546   $1,207.35   $1,207.40   $1,207.30