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 $118.86   11.128%   $132.0867   $132.09   $132.10   $132.10  
  Purchase #2 $184.74   4.126%   $192.3624   $192.36   $192.35   $192.40  
  Purchase #3 $91.60   11.749%   $102.3621   $102.36   $102.35   $102.40  
  Purchase #4 $235.56   4.569%   $246.3227   $246.32   $246.30   $246.30  
  Purchase #5 $23.48   9.311%   $25.6662   $25.67   $25.65   $25.70  
  Purchase #6 $155.71   9.848%   $171.0443   $171.04   $171.05   $171.00  
  Purchase #7 $202.94   4.856%   $212.7948   $212.79   $212.80   $212.80  
  7 purchase totals = $1,012.89       $1,082.6392   $1,082.63   $1,082.60   $1,082.70