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 $54.94   8.640%   $59.6868   $59.69   $59.70   $59.70  
  Purchase #2 $102.97   7.594%   $110.7895   $110.79   $110.80   $110.80  
  Purchase #3 $178.41   9.461%   $195.2894   $195.29   $195.30   $195.30  
  Purchase #4 $10.88   8.635%   $11.8195   $11.82   $11.80   $11.80  
  Purchase #5 $30.93   6.529%   $32.9494   $32.95   $32.95   $32.90  
  Purchase #6 $185.46   4.623%   $194.0338   $194.03   $194.05   $194.00  
  Purchase #7 $222.28   9.327%   $243.0121   $243.01   $243.00   $243.00  
  7 purchase totals = $785.87       $847.5805   $847.58   $847.60   $847.50