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 $81.36   7.674%   $87.6036   $87.60   $87.60   $87.60  
  Purchase #2 $77.62   9.787%   $85.2167   $85.22   $85.20   $85.20  
  Purchase #3 $39.38   4.325%   $41.0832   $41.08   $41.10   $41.10  
  Purchase #4 $224.58   9.771%   $246.5237   $246.52   $246.50   $246.50  
  Purchase #5 $250.84   6.755%   $267.7842   $267.78   $267.80   $267.80  
  Purchase #6 $104.43   13.496%   $118.5239   $118.52   $118.50   $118.50  
  Purchase #7 $245.82   5.281%   $258.8018   $258.80   $258.80   $258.80  
  7 purchase totals = $1,024.03       $1,105.5371   $1,105.52   $1,105.50   $1,105.50