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 $151.75   9.720%   $166.5001   $166.50   $166.50   $166.50  
  Purchase #2 $125.41   11.565%   $139.9137   $139.91   $139.90   $139.90  
  Purchase #3 $212.84   7.222%   $228.2113   $228.21   $228.20   $228.20  
  Purchase #4 $200.58   5.365%   $211.3411   $211.34   $211.35   $211.30  
  Purchase #5 $135.96   12.279%   $152.6545   $152.65   $152.65   $152.70  
  Purchase #6 $73.76   9.107%   $80.4773   $80.48   $80.50   $80.50  
  Purchase #7 $32.44   5.843%   $34.3355   $34.34   $34.35   $34.30  
  7 purchase totals = $932.74       $1,013.4335   $1,013.43   $1,013.45   $1,013.40