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 $234.89   12.542%   $264.3499   $264.35   $264.35   $264.30  
  Purchase #2 $95.67   5.280%   $100.7214   $100.72   $100.70   $100.70  
  Purchase #3 $224.37   7.303%   $240.7557   $240.76   $240.75   $240.80  
  Purchase #4 $178.55   13.113%   $201.9633   $201.96   $201.95   $202.00  
  Purchase #5 $37.91   3.360%   $39.1838   $39.18   $39.20   $39.20  
  Purchase #6 $203.65   3.463%   $210.7024   $210.70   $210.70   $210.70  
  Purchase #7 $84.57   10.736%   $93.6494   $93.65   $93.65   $93.60  
  7 purchase totals = $1,059.61       $1,151.3259   $1,151.32   $1,151.30   $1,151.30