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 $213.25   11.148%   $237.0231   $237.02   $237.00   $237.00  
  Purchase #2 $181.97   10.249%   $200.6201   $200.62   $200.60   $200.60  
  Purchase #3 $8.56   11.160%   $9.5153   $9.52   $9.50   $9.50  
  Purchase #4 $54.26   7.582%   $58.374   $58.37   $58.35   $58.40  
  Purchase #5 $147.31   5.709%   $155.7199   $155.72   $155.70   $155.70  
  Purchase #6 $211.62   3.508%   $219.0436   $219.04   $219.05   $219.00  
  Purchase #7 $164.44   7.821%   $177.3009   $177.30   $177.30   $177.30  
  7 purchase totals = $981.41       $1,057.5969   $1,057.59   $1,057.50   $1,057.50