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 $119.29   12.295%   $133.9567   $133.96   $133.95   $134.00  
  Purchase #2 $56.64   5.290%   $59.6363   $59.64   $59.65   $59.60  
  Purchase #3 $112.60   8.874%   $122.5921   $122.59   $122.60   $122.60  
  Purchase #4 $203.96   9.701%   $223.7462   $223.75   $223.75   $223.70  
  Purchase #5 $73.52   7.503%   $79.0362   $79.04   $79.05   $79.00  
  Purchase #6 $213.29   9.211%   $232.9361   $232.94   $232.95   $232.90  
  Purchase #7 $84.59   6.415%   $90.0164   $90.02   $90.00   $90.00  
  7 purchase totals = $863.89       $941.9200   $941.94   $941.95   $941.80