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 $187.79   10.472%   $207.4554   $207.46   $207.45   $207.50  
  Purchase #2 $223.79   8.733%   $243.3336   $243.33   $243.35   $243.30  
  Purchase #3 $82.52   6.800%   $88.1314   $88.13   $88.15   $88.10  
  Purchase #4 $46.65   8.839%   $50.7734   $50.77   $50.75   $50.80  
  Purchase #5 $168.93   10.496%   $186.6609   $186.66   $186.65   $186.70  
  Purchase #6 $213.66   6.715%   $228.0073   $228.01   $228.00   $228.00  
  Purchase #7 $179.97   13.256%   $203.8268   $203.83   $203.85   $203.80  
  7 purchase totals = $1,103.31       $1,208.1888   $1,208.19   $1,208.20   $1,208.20