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 $56.43   12.142%   $63.2817   $63.28   $63.30   $63.30  
  Purchase #2 $196.51   13.486%   $223.0113   $223.01   $223.00   $223.00  
  Purchase #3 $225.74   12.312%   $253.5331   $253.53   $253.55   $253.50  
  Purchase #4 $89.26   5.499%   $94.1684   $94.17   $94.15   $94.20  
  Purchase #5 $111.30   11.731%   $124.3566   $124.36   $124.35   $124.40  
  Purchase #6 $210.78   5.239%   $221.8228   $221.82   $221.80   $221.80  
  Purchase #7 $204.96   8.632%   $222.6521   $222.65   $222.65   $222.70  
  7 purchase totals = $1,094.98       $1,202.8260   $1,202.82   $1,202.80   $1,202.90