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 $87.50   11.842%   $97.8618   $97.86   $97.85   $97.90  
  Purchase #2 $202.42   4.223%   $210.9682   $210.97   $210.95   $211.00  
  Purchase #3 $114.61   3.218%   $118.2981   $118.30   $118.30   $118.30  
  Purchase #4 $157.96   12.869%   $178.2879   $178.29   $178.30   $178.30  
  Purchase #5 $41.34   3.841%   $42.9279   $42.93   $42.95   $42.90  
  Purchase #6 $87.52   9.702%   $96.0112   $96.01   $96.00   $96.00  
  Purchase #7 $224.72   9.720%   $246.5628   $246.56   $246.55   $246.60  
  7 purchase totals = $916.07       $990.9179   $990.92   $990.90   $991.00