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 $73.72   9.223%   $80.5192   $80.52   $80.50   $80.50  
  Purchase #2 $133.84   10.827%   $148.3309   $148.33   $148.35   $148.30  
  Purchase #3 $33.73   3.829%   $35.0215   $35.02   $35.00   $35.00  
  Purchase #4 $221.61   11.470%   $247.0287   $247.03   $247.05   $247.00  
  Purchase #5 $227.81   6.803%   $243.3079   $243.31   $243.30   $243.30  
  Purchase #6 $167.66   8.349%   $181.6579   $181.66   $181.65   $181.70  
  Purchase #7 $90.80   8.217%   $98.261   $98.26   $98.25   $98.30  
  7 purchase totals = $949.17       $1,034.1271   $1,034.13   $1,034.10   $1,034.10