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 $188.41   9.214%   $205.7701   $205.77   $205.75   $205.80  
  Purchase #2 $170.52   4.194%   $177.6716   $177.67   $177.65   $177.70  
  Purchase #3 $165.56   8.174%   $179.0929   $179.09   $179.10   $179.10  
  Purchase #4 $71.57   5.488%   $75.4978   $75.50   $75.50   $75.50  
  Purchase #5 $118.68   4.230%   $123.7002   $123.70   $123.70   $123.70  
  Purchase #6 $213.95   12.332%   $240.3343   $240.33   $240.35   $240.30  
  Purchase #7 $187.51   3.484%   $194.0428   $194.04   $194.05   $194.00  
  7 purchase totals = $1,116.20       $1,196.1097   $1,196.10   $1,196.10   $1,196.10